Methods: Patients who underwent abscess drainage in 3 major colorectal units between September 2005 and January 2008 were included. Previous anorectal surgery history, immunecompromised states, pregnancy, inflammatory bowel disease, antibiotic usage prior to surgery and the presence of an anal fistulae at the time of surgery were the exclusion criteria. Patients were randomized and given either placebo or amoxicillin-clavulanic acid combination treatment for 10 days. Patients were followed one year for perianal fistulae formation.